Conventionally, this kind of surface illuminating apparatus, as disclosed in, for example, the Japanese Utility Model Publication Gazette No. Sho 58-38,186, is provided at one surface of a transparent plate with a large number of fine spots, a reflecting plate is mounted on the transparent plate so as to cover the spotted surface, a light diffusion plate is brought into close contact with the other surface of the transparent plate, and a light source is disposed at the lateral end surface thereof, thereby uniformly illuminating the entire surface of the light diffusion plate.
The above-mentioned conventional example, however, includes one transparent plate which is provided at one surface thereof with the predetermined spots, so that the light incident on the transparent plate is repeatedly refracted and reflected by the spots and reflecting plate and then emitted through the light diffusion plate in a diffusing manner, the light reflected by the spots and emitted from the light diffusion plate is brighter than that which is not reflected by the spots but is repeatedly refracted and emitted from the light diffusion plate, thereby causing the brightness to be uneven.
In order to eliminate the fact that the brightness is uneven, the spots may be increased in number, but it is then difficult for the light emitted from the light source to travel to a distance, thereby causing the brightness to be uneven due to a distance from the light source. Hence, the problem is created in that the entire surface of the light diffusion plate is not yet uniformly brightened.